The invention relates to a method of controlling the quantity of air in a closed, chargeable and emptiable pneumatic level control system in a vehicle, which level control system comprises at least one pressure sensor, one pump, at least one actuator, at least one storage reservoir and circuitry connecting these assemblies, and at least one level sensor, the pressure sensor measuring the air pressure in the individual components of the level control system.
In a pneumatic level control system the actuators are generally pneumatic springs arranged on at least one vehicle axle between the individual wheel and the vehicle body. To raise the level of the vehicle body, the individual pneumatic spring is connected to a pressure source, for example a pump, which takes in air from the surroundings, or to a pressurized gas storage reservoir. To lower the level of the vehicle body, the individual pneumatic spring is connected to a pressure sink, for example the surroundings. The performance of the pump determines hereby the speed with which the level is increased. The energy expended in the process is lost when the vehicle body is lowered by discharging the air into the surroundings.
DE 100 55 108, which was published after the priority date, discloses a pneumatic suspension device having a closed compressed air system.
In this system a pressurized gas storage reservoir is connected to the pneumatic springs in order to raise the level of the vehicle body. When the vehicle body is lowered, air is returned from the pneumatic springs into the storage reservoir with or without pump assistance. An air exchange with the ambient air only takes place if the pressure differences between the individual components of the compressed air system are not sufficient for the desired change in level.
It is the object of the present invention to provide a method of controlling the quantity of air in a closed level control system, which allows the level to be controlled within the closed system in every state of the system.